https://en.wikipedia.org/wiki/Galileo_thermometer
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In some models, if there are some bulbs at the top (Figure 4, left) and some at the bottom, but one floating in the gap, then the one floating in the gap (green 76 °F (24 °C)) tells the temperature. If there is no bulb in the gap (Figure 4, right) then the average of the values of the bulb above and below the gap gives the approximate temperature. In other models, the lowest floating bulb gives the approximate temperature.[6]
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